1. Field of the Invention
The present invention relates to a plasma treatment apparatus and a plasma treatment method applied to a manufacturing process or the like of semiconductor elements such as a thin film transistor (TFT) and a metal oxide semiconductor element (MOS element), semiconductor devices such as a semiconductor integrated circuit device, or display devices such as a liquid crystal display device.
2. Description of the Related Art
A parallel plate type high-frequency plasma treatment apparatus, an electron cyclotron resonance (ECR) plasma treatment apparatus and the like have heretofore been used for performing plasma treatment such as film deposition, surface reforming and etching in a manufacturing process of a semiconductor device, liquid crystal display device or the like.
However, the parallel plate type plasma treatment apparatus has a problem that plasma density is low and electron temperature is high. Since the ECR plasma treatment apparatus requires direct-current magnetic field in plasma excitation, there has been a problem that it is difficult to treat a large area.
To solve the problem, in recent years, a plasma treatment apparatus has been proposed which does not require any magnetic field in the plasma excitation and which is capable of generating plasmas having high density and low electron temperature.
As this type of plasma treatment apparatus, an apparatus has been known comprising a circular microwave radiation plate having slots arranged in a concentric shape. This plasma treatment apparatus is constituted in such a manner that microwaves introduced from a coaxial tube toward a center of the circular microwave radiation plate propagate in a diametric direction of this circular microwave radiation plate and emanate from the slots. Accordingly, since the microwaves are introduced into a vacuum vessel via en electromagnetic wave radiation window, plasmas are generated in this vacuum vessel (see, e.g., Jpn. Pat. No. 2722070).
Moreover, as a plasma treatment apparatus, an apparatus has been known in which microwaves are supplied into a chamber from two slots constituting a waveguide antenna disposed on an H face of the rectangular waveguide via a dielectric window. In this plasma treatment apparatus, a slot width is formed to be reduced in the vicinity of a reflective face. The slot is formed into a staircase or tapered shape to narrow toward the reflective face of the waveguide (see, e.g., Jpn. Pat. No. 2857090).
Furthermore, as the plasma treatment apparatus, a surface wave plasma apparatus has been known in which a plurality of rectangular waveguides are arranged in parallel with one another at equal intervals. Coupling holes are arranged in each waveguide in such a manner that coupling coefficient is successively increased toward a tip end of the waveguide. The vacuum vessel is provided with a plurality of dielectric windows divided/formed facing the respective coupling holes (see, e.g., Jpn. Pat. Appln. KOKAI Publication No. 2002-280196).
However, as in the plasma treatment apparatus described in the Jpn. Pat. No. 2722070, when the microwaves propagate through conductors, for example, the coaxial tube and the circular microwave radiation plate, propagation loss such as copper loss is generated in these conductors. When frequency increases, or coaxial transmission distance or radiation plate area increases, the propagation loss increases. Therefore, even when the plasma treatment apparatus for a comparatively large substrate of the liquid crystal display device or the like is designed using the technique described in the Jpn. Pat. No. 2722070, decay of the microwaves increases, and it is difficult to generate the plasmas with good efficiency. Since the plasma treatment apparatus described in the Jpn. Pat. No. 2722070 is constituted to radiate the microwaves from the circular microwave radiation plate, there has been a problem that the plasmas become non-uniform in corner portions of the substrate in application to the square substrate like the liquid crystal display device.
Moreover, in a case where the microwaves that have propagated through the rectangular waveguide are radiated from two slots as in the plasma treatment apparatus described in the Jpn. Pat. No. 2857090, when many negative ions exist in the generated plasmas, there is a problem that opposite-polarity diffusion coefficient of the plasma decreases. Therefore, in the technique described in the Jpn. Pat. No. 2857090, the plasmas are generated only in the vicinity of the slots from which the microwaves are radiated. This eccentricity of the plasma becomes remarkable especially in a case where pressure of the plasma is high. Therefore, in the plasma treatment apparatus described in the Jpn. Pat. No. 2857090, it is difficult to subject the large-sized substrate to the plasma treatment using, as a raw material, a gas containing oxygen, hydrogen, chlorine and the like in which the negative ions are easily generated, and this is further difficult especially in a case where the gas pressure is high. Furthermore, since distribution of the slots constituting the waveguide antenna is localized (non-uniform) with respect to the treated face of the substrate subjected to the plasma treatment, plasma density easily becomes non-uniform.
Additionally, in the technique described in the Jpn. Pat. No. 2722070 or 2857090, the electromagnetic wave radiation window (dielectric window) needs to be designed into a thickness (strength) which bears a gas pressure difference between a substantially atmospheric pressure and a substantially/approximately vacuum pressure, that is, a force of about 1 kg/cm2. In general, a process gas or the like is introduced into the vacuum vessel after once evacuating the vacuum vessel (chamber) in a case where the plasma treatment is performed. Therefore, when the plasma treatment apparatus for plasma-treating a large-sized substrate having a size of 1 m square is designed using the technique described in the Jpn. Pat. No. 2722070 or 2857090, the thickness of the electromagnetic wave transmission window formed of quartz or the like becomes very large, and this is not practical.
Furthermore, in the technique described in the Jpn. Pat. Appln. KOKAI Publication No. 2002-280196, since the waveguides are arranged at intervals, it is difficult to uniformly distribute the coupling holes facing the whole treated face of a substrate to be treated. Since seals for sealing vacuum need to be disposed as many as the coupling holes, a structure of the vacuum vessel is easily complicated. Additionally, since a processing cost of a top plate of the vacuum vessel increases, there is also a problem that an apparatus price increases.
The present applicant has proposed that a waveguide be disposed in a vacuum vessel as the plasma treatment apparatus having a simple structure and capable of satisfactorily plasma-treating even the component to be treated, for example, the square substrate or the large-area substrate (see Jpn. Pat. Appln. No. 2002-366842).
Additionally, in the Jpn. Pat. Appln. No. 2002-366842, an example has been described in which the waveguide is filled with a conductor component in order to inhibit invasion of the plasmas into the waveguide. However, when the waveguide is filled with the conductor component, and the waveguide disposed in the vacuum vessel is coupled to an oscillator for oscillating an electromagnetic wave via a waveguide disposed outside the vacuum vessel, a part of the electromagnetic waves is reflected in a boundary between the waveguide outside the vacuum vessel and that in the vacuum vessel, and transmittance of the electromagnetic wave drops. For example, in a case where the waveguide outside the vacuum vessel is filled with air (dielectric constant ∈=1), and the waveguide in the vacuum vessel is filled with quartz (dielectric constant ∈=3.8), when a plane wave vertically enters the boundary, the transmittance is about 80%.
The present invention has been developed based on this situation, and an object thereof is to provide a plasma treatment apparatus and a plasma treatment method capable of simplifying a structure, generating uniform plasmas having large areas, or efficiently transmitting electromagnetic waves.